Combined imaging coded data source data acquisition

ABSTRACT

A signal processing means ( 40 ) outputs a signal ( 41 ) representing a number when a combination of at least two imagers ( 11 ), ( 12 ) detects a spatial arrangement of a plurality of code portions of a coded data source (60)—where the spatial arrangement of the plurality of code portions represents the number, and where imager combinations can comprise spatial, temporal, and light property combinations.

[0001] This application claims benefit of U.S. provisional applications60/284,836 filed 19 Apr. 2001, 60/292,113 filed 18 May 2001, and60/308,699 filed 30 Jul. 2001.

[0002] A signal processing means 40 outputs a signal 41 representing anumber when a combination of at least two imagers 11, 12 detects aspatial arrangement of a plurality of code portions of a coded datasource 60—where the spatial arrangement of the plurality of codeportions represents the number, and where imager combinations cancomprise spatial, temporal, and light property combinations.

[0003]FIG. 1 schematically depicts the product.

[0004]FIG. 2 depicts two imager fields of view 21, 22.

[0005]FIG. 3 depicts three adjacent imager fields of view 21A, 22A, 23A.

[0006] The data acquisition product comprises a first imager 11 whichhas a first imager field of view, comprises a second imager 12 which hasa second imager field of view, comprises a first coded data source 60,and comprises signal processing means 40.

[0007] The first coded data source has at least a first spatialarrangement of a first plurality of first code portions. The firstspatial arrangement of the first plurality of first code portionsrepresents at least a first number.

[0008] The first coded data source emanates first light. The first lightrepresents the first spatial arrangement of the first plurality of codeportions. The first light is detected by the first imager if the firstlight is from the first imager field of view and is not occluded. Thefirst light is detected by the second imager if the first light is fromthe second imager field of view and is not occluded.

[0009] The first coded data source can be a member from a plurality ofcoded data sources each having at least a member specific spatialarrangement of a plurality of first code portions representing at leasta member specific number. Coded data sources can be as described inpatent application PCTUS/01/13742 filed 30 Apr. 2001 and published as WO01/84475 on 08 Nov. 2001 which is incorporated herein by reference.

[0010] Member specific light from any member from the plurality of codeddata sources represents at least the member specific spatial arrangementof the plurality of coded data sources, and, thus, represents at leastthe member specific number.

[0011] The signal processing means is signal connected with the firstimager. The signal processing means is signal connected with the secondimager. The signal processing means is adapted to cause a signal 41which represents the first number.

[0012] The signal processing means causes the signal if a combination ofthe first imager and the second imager detects the first spatialarrangement of the first plurality of code portions. The signal need notbe an image of the first coded data source, nor be an image of the firstspatial arrangement of the first plurality of code portions, the signalneed only represent the first number.

[0013] The signal processing means can also cause a coordinate signalwhich represents coordinates of coded data sources relative to somereferent. The signal processing means can also cause other signalsrepresenting various spatial, temporal, and light property features ofcoded data sources and of imagers.

[0014] The first imager can detect light concurrently from manyspatially separated coded data sources from the plurality of coded datasources—for example 60, 70—in the first imager field of view—for example20. At least the first imager can represent, for the signal processingmeans, the member specific light from each and all of these coded datasources. The second imager can detect light from many coded datasources—for example 60, 70—in the second imager field of view—forexample 20.

[0015] At least the first imager field of view can be dense with theplurality of coded data sources. At least an occluded member from theplurality of coded data sources can be occluded. If light from membersfrom the plurality of coded data sources surrounding the occluded codeddata source is from the first imager field of view and is not occluded,the first imager can represent the absence of the occluded member forthe signal processing means. If light from members of the plurality ofdata sources surrounding the occluded member is from the second imagerfield of view and is not occluded, the second imager can represent theabsence of the occluded member for the signal processing means. In thiscase the signal processing means can cause the signal to represent thenumber represented by the occluded coded data source. When these codeddata sources have known locations (which can be fixed and can moving)this signal also represents the location of the occluded coded datasource.

[0016] Coded data sources can be poles with the member specific spatialarrangements of a plurality of code portions symmetric with respect torotation abut the pole long axis. The poles need not be densely located.When the poles are in the fields of view of several imagers, the firstimager is an imager for which a first pole is temporarily occluded bysomething moving past a pole, the second imager is an imager which isnot occluded by the something, then the signal represents the memberspecific spatial arrangement of a plurality of code portions of thefirst pole. When these coded data sources have known locations (whichcan be fixed and can moving) this signal also represents the location ofthe first pole.

[0017] Light from any coded data source can represent the memberspecific spatial arrangement of a plurality of code portions by means ofvarious physical properties of light in fixed, variable, and modulatedmodes. These physical properties of light comprise intensities,frequencies, phases, polarizations, entanglements, blink rates, decaytimes, external shapes, internal shapes, linear motions, rotationalmotions, strain motions, distances from at least one reference point,and combinations of physical properties such as these. A spatialarrangement of a plurality of code portions can represent a number by aspatial arrangement of physical properties such as these in fixed,variable, and modulated modes.

[0018] For example, a number can be represented by a spatial arrangementof color bands such as those shown 60, 80. For example, a number can berepresented by a spatial arrangement of a series of bars—for exampleretro-reflecting infra red—where the bars each have a long axis longerthan a lateral axis such as shown 70. For example, a vertical bar canrepresent 1 and a horizontal bar can represent 0 so that the number isrepresented by binary coding. The ways of representing a number arelimited only by light properties and possible spatial arrangementsthereof.

[0019] Light from a coded data source can have various origins such aslight reflected from ambient sources, a light source at the coded datasource, light emitted after energizing by suitable radiation, light witha characteristic decay time emitted after energizing by suitableradiation, a light source adjacent to the imager illuminating the codeddata source, and combinations of sources such as these.

[0020] Light from a coded data source is not limited to visible light.For example, infrared can be used, and millimeter and longer wavelengthscan be used. Light can be radiating energy from any portion of theelectromagnetic spectrum which can provide the functions required here.Other forms of radiating energy—such as acoustic energy—which canprovide the functions required here are included in the meaning of“light” here.

[0021] There can be a plurality of imagers each being interchangeablewith the first imager. There can be a plurality of imagers each beinginterchangeable with the second imager. A first imager can be a firstportion of an imager and a second imager can be a second portion of theimager. A first imager can be an imager operating at a first time and asecond imager can be the imager operating at a second time separate fromthe first time. A first imager can be an imager operating at a firstposition and a second imager can be the imager operating at a secondposition separate from the first position.

[0022] Various imagers can be used in various modes of operation toprovide the functions needed here of the first imager, the secondimager, and any subsequent imager. Any of-and all of-the first imager,the second imager, and their respective equivalents can be the dual modeimager of patent application PCTUS/01/13742 filed 30 Apr. 2001 andpublished as WO 01/84475 on 08 Nov. 2001.

[0023] “Detect light” here and throughout means not only detecting thepresence of light but also means detecting the specific properties ofthe light which represent a specific spatial arrangement of a pluralityof code portions so that the imager can represent the specific spatialarrangement of a plurality of code portions for the signal processingmeans. Detecting light concurrently from several spatially separatedcoded data sources distinguishes the imager from devices such as barcode readers which can not concurrently detect light from severalspatially separated bar codes within the meaning of “detect” here.

[0024] A “signal” from a first product part to a second product part anda first product part being “signal connected” with a second product parthere, and throughout, mean that a first physical state of the firstproduct part causes a second physical state of the second product part.This can occur by various direct causal means and can occur by any ofvarious transmission means. Transmitted signals can be any of variouspoint-to-point and broadcast forms of energy transmission such aswireless and via wires, cables, and fibers. Parts of transmitted signalscan reside with one form of the transmitted signal, parts can residewith a second form of transmitted signal, and parts can reside withvarious combinations of transmitted signals.

[0025] The several causes and representations here can act via any ofvarious processing means. The processing can utilize configuredprocessing elements such as fixed circuits, can utilize configurableprocessing elements such as field programmable gate arrays and neuralnetworks, can utilize instructions in a data-bearing medium, and canutilize combinations of these. The processing can be stand alone, canact via a local information system, can act via a networked informationsystem, and can act via combinations of these.

[0026] A signal representing the first number-and any subsequentnumbers-is caused by the signal processing means when an imagercombination detects the first spatial arrangement of the first pluralityof code portions of the first coded data source-and detects anysubsequent member specific arrangements of pluralities of code portionsof any subsequent coded data sources. Imager combinations arecombinations of at least two imagings. The imagings can be by the firstimager and the second imager for example. What is true of first imagerand second imager combinations is true of combinations of more than twoimagings. Imager combinations can comprise several spatial, temporal,and light property combinations in order to detect a spatial arrangementof a plurality of code portions.

[0027] In an imager combination, the second imager causes the firstfield of view to include the first coded data source if the first lightis from the second imager field of view and is not occluded, and thefirst imager causes the first light to be represented for the signalprocessing means.

[0028] For example, if the coded data source is not in the first imagerfield of view when the second imager detects the presence of the firstlight, then the second imager can cause the first imager field of viewto change until the first data source is in the first imager field ofview.

[0029] In this combination, the second imager can have a second imagerfield of view more than twice larger area-wise than the first imagerfield of view. The second imager can be a low resolution imager. Thefirst imager field of view can be caused to include little more than thefirst coded data source. The second imager can be sensitive to only anarrow range of one-and more-light properties.

[0030] In this combination the first imager can be a sub system of thesecond imager. For example, the second imager can be a full detectionarea and the first imager can be a part of the full detection area.

[0031] In an imager combination, the first imager causes a first lightproperty portion of the first light to be represented for the signalprocessing means if the first light is from the first imager field ofview and is not occluded. The second imager causes a second lightproperty portion of the first spatial arrangement of the first light tobe represented for the signal processing means if the first light isfrom the second imager field of view and is not occluded. The signalprocessing means uses the first light property portion caused to berepresented and the second light property portion caused to berepresented to cause the signal.

[0032] The first and second light property portions can be portions ofthe various physical light properties described above. For example, thefirst light property portion can be a first frequency portion and thesecond light property portion can be a second frequency portion. In thisexample the first frequency portion can be red light, the secondfrequency portion can be green light, and a third frequencyportion—represented for the signal processing means by a third imager ifthe first light is from the third imager field of view—can be bluelight.

[0033] In an imager combination, the first imager causes a firstrepresentation of the first light to be represented for the signalprocessing means at a first time if the first light is from the firstimager field of view and is not occluded at the first time. The secondimager causes a second representation of the first light to berepresented for the signal processing means at a second time if thefirst light is from the second imager field of view and is not occludedat the second time. The signal processing means uses the firstrepresentation and the second representation to cause the signal torepresent the first number at the first time and the second time.

[0034] For example, there can be an array of N imagers comprising thefirst imager, the second imager, and subsequent imagers. The array viewsa field of view. Each member imager in the array views a member specificimager field of view. Each member specific imager field of view canfully overlap the full field of view. There can be various relationsamong the member specific imager fields of view so long the whole arraycan comprehend the full field of view.

[0035] The N imagers each begin imaging with time delays between imagersof 1/N of the 1/T imaging frequency of each imager. Thus, in an N equals4 case, the first imager begins imaging at times T, 2T, 3T, etc.; thesecond imager begins imaging at times T(1+¼), T(2+¼), T(3+¼), etc.; athird imager begins at times T(1+{fraction (2/4)}), T(2+{fraction(2/4)}), T(3+{fraction (2/4)}), etc.; and a fourth imager begins attimes T(1+¾), T(2+¾), T(3 +¾), etc. This yields an effective imagingfrequency of 4/T for the whole array.

[0036] In an imager combination, the second imager field of view isadjacent to the first imager field of view. The first imager causes afirst portion of the first light to be represented for the signalprocessing means if the first portion of the first light is from thefirst imager field of view and is not occluded. The second imager causesa second portion of the first light to be represented for the signalprocessing means if the second portion of the first light is from thesecond imager field of view and is not occluded. The signal processingmeans uses the first portion caused to be represented and the secondportion caused to be represented to cause the signal.

[0037]FIG. 3 depicts three adjacent imager fields of view 21A, 22A, 23A.The first imager field of view 21A slightly overlaps the second imagerfield of view 22A. The second imager field of view abuts a third imagerfield of view 23A. Slightly overlapping and abutting are both includedin the meaning of “adjacent” here.

[0038] In an imager combination, the first imager detects light byscanning substantially parallel to first axis 101. The second imagerdetects light by scanning substantially parallel to a second axis 102.The first axis is not parallel to the second axis. The first imagercauses the first spatial arrangement of the first plurality of codeportions to be represented for the signal processing means as soon asthe first spatial arrangement of the first plurality of code portions isdetected by the first imager, if the first spatial arrangement of thefirst plurality of code portions is detected by the first imager. Thesecond imager causes the first spatial arrangement of the firstplurality of code portions to be represented for the signal processingmeans as soon as the first spatial arrangement of the first plurality ofcode portions is detected by the second imager, if the first spatialarrangement of the first plurality of code portions is detected by thesecond imager. The signal processing means uses the first in time firstspatial arrangement of the first plurality of code portions caused to berepresented to cause the signal.

[0039]FIG. 2 depicts a coded data source 80 in the first imager field ofview 21 and in the second imager field of view 22. The first imager,scans substantially parallel to axis 101. The second imager scanssubstantially parallel to axis 102. The first imager will detect thespatial arrangement of the plurality of code portions of the coded datasource 80 before the second imager scans enough of the spatialarrangement to detect the spatial arrangement. A plurality of imagersscanning along non-parallel axes will minimize the time to acquire dataand will eliminate the need to orient the imager—or the coded datasource—to detect the spatial arrangement.

[0040] In an imager combination, the first light is at least partiallyretro-reflected from a light source. The first imager, the secondimager, and the fight source are positioned so that more first light isretro-reflected to the first imager than to the second imager. The firstimager causes a first representation of the first light to berepresented along with all light detected by the first imager for thesignal processing means if the first light is from the first imagerfield of view and is not occluded. The second imager causes a secondrepresentation of the first light to be represented along with all lightdetected by the second imager for the signal processing means if thefirst light is from the second imager field of view and is not occluded.The signal processing means uses the first representation and the secondrepresentation to represent the first number. The signal processingmeans also uses all light caused to be represented by the first imagerand all light caused to be represented by the second imager to cause thesignal.

[0041] In this combination the retro-reflected light detected by thefirst imager will be more intense than the retro-reflected lightdetected by the second imager. Both imagers may detect light notemanating from the first coded data source. Subtraction of all lightcaused to be represented by the second imager from all light caused tobe represented by the first imager reduces the light not from the firstcoded data source represented for the signal processing means.

1. A data acquisition product comprising: a first imager, the firstimager having a first imager field of view; a second imager, the secondimager having a second imager field of view; a first coded data source,the first coded data source having a first spatial arrangement of afirst plurality of first code portions, the first spatial arrangement ofthe first plurality of first code portions representing a first number;first light representing the first spatial arrangement of the firstplurality of code portions, first light being detected by the firstimager if the first light is from the first imager field of view and isnot occluded, first light being detected by the second imager if thefirst light is from the second imager field of view and is not occluded;and signal processing means, the signal processing means being signalconnected with the first imager, the signal processing means beingsignal connected with the second imager, the signal processing meansbeing adapted to cause a signal which represents the first number, andthe signal processing means causing the signal if a combination of thefirst imager and the second imager detects the first spatial arrangementof the first plurality of code portions.
 2. The product of claim 1wherein: the second imager causes the first imager field of view toinclude the first coded data source if the first light is from thesecond imager field of view and is not occluded; and the first imagercauses the first light to be represented for the signal processingmeans.
 3. The product of claim 1 wherein: the first imager causes afirst representation of a first light property portion of the firstlight to be represented for the signal processing means if the firstlight is from the first imager field of view and is not occluded; thesecond imager causes a second representation of a second light propertyportion of the first light to be represented for the signal processingmeans if the first light is from the second imager field of view and isnot occluded; and the signal processing means uses the firstrepresentation and the second representation to cause the signal.
 4. Theproduct of claim 3 wherein the first light property portion is a firstfrequency portion and the second light property portion is a secondfrequency portion.
 5. The product of claim 1 wherein: the first imagercauses a first representation of the first light to be represented forthe signal processing means at a first time if the first light is fromthe first imager field of view and is not occluded at the first time;the second imager causes a second representation of the first light tobe represented for the signal processing means at a second time if thefirst light is from the second imager field of view and is not occludedat the second time; and the signal processing means uses the firstrepresentation and the second representation to cause the signal torepresent the first number at the first time and the second time. 6.Then product of claim 1 wherein: the second imager field of view isadjacent to the first imager field of view; the first imager causes afirst portion of the first spatial arrangement of the first plurality ofcode portions to be represented for the signal processing means if thefirst portion of the first spatial arrangement of the first plurality ofcode portions is in the first imager field of view; the second imagercauses a second portion of the first spatial arrangement of the firstplurality of code portions to be represented for the signal processingmeans if the second portion of the first spatial arrangement of thefirst plurality of code portions is in the second imager field of view;and the signal processing means uses the first portion caused to berepresented and the second portion caused to be represented to cause thesignal.
 7. The product of claim 1 wherein: the first imager detectslight by scanning substantially parallel to first axis; the secondimager detects light by scanning substantially parallel to a secondaxis; the first axis is not parallel to the second axis; the firstimager causes the first spatial arrangement of the first plurality ofcode portions to be represented for the signal processing means as soonas the first spatial arrangement of the first plurality of code portionsis detected by the first imager, if the first spatial arrangement of thefirst plurality of code portions is detected by the first imager; thesecond imager causes the first spatial arrangement of the firstplurality of code portions to be represented for the signal processingmeans as soon as the first spatial arrangement of the first plurality ofcode portions is detected by the second imager, if the first spatialarrangement of the first plurality of code portions is detected by thesecond imager; and the signal processing means uses the first in timespatial arrangement of the first plurality of code portions caused to berepresented to cause the signal.
 8. The product of claim 1 wherein: thefirst light is at least partially retro-reflected from a light source;the first imager, the second imager, and the light source are positionedso that more first light is retro-reflected to the first imager than tothe second imager; the first imager causes a first representation of thefirst light to be represented for the signal processing means if thefirst light is from the first imager field of view and is not occluded;the second imager causes a second representation of the first light tobe represented for the signal processing means if the first light isfrom the second imager field of view and is not occluded; and the signalprocessing means uses the first representation and the secondrepresentation to cause the signal
 9. A data acquisition productcomprising: a first image, the first imager having a first imager fieldof view; a second imager, the second imager having a second imager fieldof view; a first coded data source, the first coded data source having afirst spatial arrangement of a first plurality of first code portions,the first spatial arrangement of the first plurality of first codeportions representing a first number; first light representing the firstspatial arrangement of the first plurality of code portions, first lightbeing detected by the first imager if the first light is from the firstimager field of view and is not occluded, first light being detected bythe second imager if the first light is from the second imager field ofview and is not occluded; and signal processing means, the signalprocessing means being signal connected with the first imager, thesignal processing means being signal connected with the second imager,the signal processing means being adapted to cause a signal whichrepresents the first number, the second imager causing the first imagerfield of view to include the first coded data source if the first lightis from the second imager field of vies and is not occluded, the firstimager causing the first light to be represented for the signalprocessing means, and the signal processing means causing the signalwhen the first imager causes the first light to be represented for thesignal processing means.
 10. A data acquisition product comprising: afirst imager, the first imager having a first imager field of view; asecond imager, the second imager having a second imager field of view; afirst coded data source, the first coded data source having a firstspatial arrangement of a first plurality of first code portions, thefirst spatial arrangement of the first plurality of first code portionsrepresenting a first number; first light representing the first spatialarrangement of the first plurality of code portions, first light beingdetected by the first imager if the first light is from the first imagerfield of view and is not occluded, first light being detected by thesecond imager if the first light is from the second imager field of viewand is not occluded; and signal processing means, the signal processingmeans being signal connected with the first imager, the signalprocessing means being signal connected with the second imager, thesignal processing means being adapted to cause a signal which representsthe first number, the first imager causing a first representation of afirst light property portion of the first light to be represented forthe signal processing means if the first light is from the first imagerfield of view and is not occluded; the second imager causing a secondrepresentation of a second light property portion of the first light tobe represented for the signal processing means if the first light isfrom the second imager field of view and is not occluded; and the signalprocessing means using the first representation and the secondrepresentation to cause the signal.
 11. A data acquisition productcomprising: a first imager, the first imager having a first imager fieldof view; a second imager, the second imager having a second imager fieldof view; a first coded data source, the first coded data source having afirst spatial arrangement of a first plurality of first code portions,the first spatial arrangement of the first plurality of first codeportions representing a first number; first light representing the firstspatial arrangement of the first plurality of code portions, first lightbeing detected by the first imager if the first light is from the firstimager field of view and is not occluded, first light being detected bythe second imager if the first light is from the second imager field ofview and is not occluded; and signal processing means, the signalprocessing means being signal connected with the first imager, thesignal processing means being signal connected with the second imager,the signal processing means being adapted to cause a signal whichrepresents the first number, the first imager causing a firstrepresentation of the first light to be represented for the signalprocessing means at a first time if the first light is from the firstimager field of view and is not occluded at the first time; the secondimager causing a second representation of the first light to berepresented for the signal processing means at a second time if thefirst light is from the second imager field of view and is not occludedat the second time; and the signal processing means using the firstrepresentation and the second representation to cause the signal torepresent the first number at the first time and the second time.
 12. Adata acquisition product comprising: a first imager, the first imagerhaving a first imager field of view; a second imager, the second imagerhaving a second imager field of view; a first coded data source, thefirst coded data source having a first spatial arrangement of a firstplurality of first code portions, the first spatial arrangement of thefirst plurality of first code portions representing a first number;first light representing the first spatial arrangement of the firstplurality of code portions, first light being detected by the firstimager if the first light is from the first imager field of view and isnot occluded, first light being detected by the second imager if thefirst light is from the second imager field of view and is not occluded;and signal processing means, the signal processing means being signalconnected with the first imager, the signal processing means beingsignal connected with the second imager, the signal processing meansbeing adapted to cause a signal which represents the first number, thesecond imager field of view being adjacent to the first imager field ofview; the first imager causing a first portion of the first spatialarrangement of the first plurality of code portions to be representedfor the signal processing means if the first portion of the firstspatial arrangement of the first plurality of code portions is in thefirst imager field of view; the second imager causing a second portionof the first spatial arrangement of the first plurality of code portionsto be represented for the signal processing means if the second portionof the first spatial arrangement of the first plurality of code portionsis in the second imager field of view; and the signal processing meansusing the first portion caused to be represented and the second portioncaused to be represented to cause the signal.
 13. A data acquisitionproduct comprising: a first imager, the first imager having a firstimager field of view; a second imager, the second imager having a secondimager field of view; a first coded data source, the first coded datasource having a first spatial arrangement of a first plurality of firstcode portions, the first spatial arrangement of the first plurality offirst code portions representing a first number; first lightrepresenting the first spatial arrangement of the first plurality ofcode portions, first light being detected by the first imager if thefirst light is from the first imager field of view and is not occluded,first light being detected by the second imager if the first light isfrom the second imager field of view and is not occluded; and signalprocessing means, the signal processing means being signal connectedwith the first imager, the signal processing means being signalconnected with the second imager, the signal processing means beingadapted to cause a signal which represents the first number, the firstimager detecting light by scanning substantially parallel to first axis;the second imager detecting light by scanning substantially parallel toa second axis; the first axis being not parallel to the second axis; thefirst imager causing the first spatial arrangement of the firstplurality of code portions to be represented for the signal processingmeans as soon as the first spatial arrangement of the first plurality ofcode portions is detected by the first imager, if the first spatialarrangement of the first plurality of code portions is detected by thefirst imager; the second imager causing the first spatial arrangement ofthe first plurality of code portions to be represented for the signalprocessing means as soon as the first spatial arrangement of the firstplurality of code portions is detected by the second imager, if thefirst spatial arrangement of the first plurality of code portions isdetected by the second imager; and the signal processing means using thefirst in time spatial arrangement of the first plurality of codeportions caused to be represented to cause the signal.
 14. A dataacquisition product comprising: a first imager, the first imager havinga first imager field of view; a second imager, the second imager havinga second imager field of view; a first coded data source, the firstcoded data source having a first spatial arrangement of a firstplurality of first code portions, the first spatial arrangement of thefirst plurality of first code portions representing a first number;first light representing the first spatial arrangement of the firstplurality of code portions, first light being detected by the firstimager if the first light is from the first imager field of view and isnot occluded, first light being detected by the second imager if thefirst light is from the second imager field of view and is not occluded;and signal processing means, the signal processing means being signalconnected with the first imager, the signal processing means beingsignal connected with the second imager, the signal processing meansbeing adapted to cause a signal which represents the first number, thefirst light being at least partially retro-reflected from a lightsource; the first imager, the second imager, and the light source beingpositioned so that more first light is retro-reflected to the firstimager than to the second imager; the first imager causing a firstrepresentation of the first light to be represented for the signalprocessing means if the first light is from the first imager field ofview and is not occluded; the second imager causing a secondrepresentation of the first light to be represented for the signalprocessing means if the first light is from the second imager field ofview and is not occluded; and the signal processing means using thefirst representation and the second representation to cause the signal.